1. Field of the Invention
The invention relates to a mold clamping apparatus and a mold clamping method, and more particularly a mold clamping apparatus for closing and holding molds in which mold opening force is generated by providing inside thereof with a pressure for opening the mold and a mold clamping method using the same.
2. Description of the Related Art
For example, in hydraulic pressure bulging processing, with both ends of a material pipe sealed, the material pipe is formed to a predetermined shape by expanding a diameter thereof or the like by raising the pressure of the liquid charged inside. Generally, the hydraulic pressure bulging processing apparatus comprises high pressure liquid supply device which supplies liquid such as water at a high pressure to the inside of the material pipe, a mold for capturing the periphery of the material pipe and axially pressing device which presses ends of the material pipe in the axial direction. The mold in the hydraulic pressure bulging processing apparatus is divided for accommodating the material pipe inside and taking out a molded product by the hydraulic pressure bulging processing. When carrying out the hydraulic pressure bulging processing by expanding the diameter of the material pipe or the like, a force intending to open the mold (mold opening force) is generated by the pressure of the liquid supplied to the inside of the material pipe. Thus, the mold is provided with a mold clamping apparatus in order to open/close the mold and hold the mold (mold clamping) in a closed state resisting a pressure applied forcing the mold to be opened during molding. As the mold clamping apparatus, generally, a general-purpose hydraulic press has been used. This general-purpose hydraulic press has a sufficiently large capacity with a huge ram and bed so as to be capable of coping with molds of various sizes. In such a general-purpose hydraulic press, columns are erected to support a crown receiving a pressure applied by the ram (for example, see Japanese Patent Laid-Open Publication No. HEI 5-329693).
Products molded by hydraulic pressure bulging processing include not only a straight product also but curved or bent products. Thus, as shown in FIG. 37, the mold 2 is also formed in a curved or bent shape. The hydraulic pressure bulging processing apparatus may be provided with axially pressing device 22 which presses ends of a material pipe in the axial direction, which is provided on ends of the mold 2 such that it is inclined with respect thereto as shown in FIG. 36.
The hydraulic pressure bulging processing may include a case of forming a T-shaped branch pipe from a straight material. In this case, the mold 2 is provided with a back pressure counter cylinder 26 for controlling a back pressure of the branch pipe to be formed, as shown in FIG. 34. The mold 2 includes a portion 2a for accommodating a straight material pipe W and a portion 2b for forming the branch pipe. The axially pressing devices 22 are provided on both end portions of the portion 2a for accommodating the material pipe W. The back pressure counter cylinder 26 is provided at an end of the portion 2b in which the branch pipe is to be formed, such that it is protruded from the mold 2. When forming the branch pipe, first, as shown in FIG. 34A, the material pipe W is disposed in the mold 2 and then, both ends thereof are sealed with the axially pressing devices 22. Liquid such as water is supplied at a high pressure through ends of the material pipe W into the inside thereof from high pressure liquid supply device (not shown) through the axially pressing devices 22, and both ends of the material pipe W are pressed with the axially pressing devices 22. Consequently, as shown in FIG. 34B, the material pipe W is expanded into the portion 2b in which the branch pipe is to be formed. At this time, growth of the branch pipe is controlled with a piston 26a of the back pressure counter cylinder 26 pressing an end of the branch pipe so that a top portion of the expanded branch pipe is not ruptured, such that the piston 26a is retreated synchronously with a supply of liquid into the material pipe W by the high pressure liquid supply device and pressing on both ends of the material pipe W by the axially pressing devices 22, as shown in FIG. 34C.
When drilling a hole in a molded product W′, a hole punch 24 (see FIG. 1) is provided in the mold 22 and as shown in FIG. 38, driving cylinders 25 for the hole punch 24 are provided so as to be protruded from the mold 2. Further, a cylinder for driving an ejector may be provided so as to be protruded from the mold 2 in order to take out the molded product W′ from an opened mold 2 (not shown). Device each having a specified function necessary for molding such as the back pressure counter cylinder 26, the driving cylinder 25 for the hole punch 24 and a driving cylinder for the ejector are referred to as functional devices.
As for a press frame, as disclosed in Japanese Utility Model No. 5-44396, and the like, a frame 101 having a holed section constructed by laminating plural sheet-like frame materials 112 whose center portion is cut out has been well known (FIG. 39). A central cut-out portion 115 in the press frame disclosed in Japanese Utility Model No. 5-44396 contains a pressure applying cylinder, a pressure receiving member and a mold although a representation thereof is omitted in FIG. 39.
In the hydraulic pressure bulging processing apparatus of the above-described related art, a general-purpose hydraulic press is employed as a mold clamping apparatus. The hydraulic press is provided with a huge ram and bed and further, the entire equipment of the hydraulic press is of a huge construction because it employs a robust structure for preventing distortion of the ram and bed, and the equipment cost becomes accordingly high. Consequently, a large area and height for installing such huge equipment is necessary and further, not only a large amount of operating energy is also necessary, but also there is a problem that the hydraulic pump always has to be driven thereby inducing an energy loss. Further, the hydraulic press takes a long time for opening/closing the mold because the ram is huge. Still further, because in the general-purpose hydraulic press used as a mold clamping apparatus, columns for supporting the ram, crown and the like are erected, it is difficult to secure a good working efficiency in carrying the material pipe W into the mold and taking out a molded product W′.
In the press frame having a closed section whose central portion is cut out as disclosed in Japanese Utility Model NO. 5-44396, for example, its central cutout portion is provided with a pressure applying cylinder and a pressure-receiving member. If this press frame having the closed section is applied to the mold clamping apparatus for the hydraulic pressure bulging processing or the like, the central cut-out portion in the press frame needs to be formed large enough for the pressure applying cylinder to be capable of opening/closing the mold and therefore, the entire size of the press frame becomes large, which is a problem to be solved. In this case, hydraulic pressure driving device and pressure application control device that drives the pressure applying cylinder need to be provided separately from the high pressure liquid supply device that supplies liquid such as water at a high pressure to the inside of the material pipe. Thus, there is a problem that equipment cost is increased and maintenance for the hydraulic driving device is necessary, and it is necessary to control the hydraulic driving device so as to drive the pressure applying cylinder accurately as set up.
In case of the press frame formed to have this closed section, if the central cut-out portion is not provided with any pressure applying cylinder and instead, the mold 2 is held directly by the frame 101 as shown in FIG. 35, the mold 2 can be inserted or taken out only in the longitudinal direction with respect to the frame 101, because the frame 101 is formed with the closed section whose central portion is cut out. Therefore, installation length L has to be as long as a sum of the length of the frame 101 and the length of the mold 2. Further, because the quantity of moving of the mold 2 is increased, it is difficult to reduce the cycle time.
If the mold 2 held by the central cut-out portion 115 in the frame 101 has the axially pressing devices 22 which is inclined with respect to the mold, the central cut-out portion 115 in the frame 101 has to be formed large enough for the axially pressing devices 22 to be capable of passing through as shown in FIG. 36. Therefore, the entire frame 101 needs to be formed sufficiently large. In this case also, the mold needs to be formed with a height T far larger than necessary for the mold 2 to be held by the central cut-out portion 115 formed large (see a portion above two-dot and dash line in FIG. 36)
If a product to be molded by the hydraulic pressure bulging processing is a curved or bent product, the central cut-out portion 115 having a width S allowing a maximum width of the curved or bent mold 2 needs to be formed in the frame 101 as shown in FIG. 37 and therefore, the entire frame 101 has to be formed large.
In case where as shown in FIG. 38, the mold 2 is provided with the functional device such as the back pressure counter cylinder 26, the driving cylinder 25 of the hole punch 24 and the ejector also, the central cut-out portion 115 with a width S which allows the functional device such as the back pressure counter cylinder 26, the driving cylinder 25 of the hole punch 24 and the ejector, protruded from the mold 2 to pass through needs to be formed. As a result, the entire frame 101 has to be formed large.
The frame 101 constructed by laminating sheet-like frame materials 112 whose central portion is cut out as disclosed in Japanese Utility Model No. 5-44396 has a closed section as shown in FIG. 39. Therefore, it is difficult to insert a grinding apparatus and carry out post processing for the central cutout portion 115 to have a smooth surface when the frame materials 112 are laminated. Thus, there is a problem that the central cutout portion 115 in each frame material 112 has to be positioned at a high precision when laminating the frame materials to form a frame.